MVC website doesn't receive string from client

Question

Client:

WebClient wc = new WebClient();
try
{
    string json = wc.UploadString("http://localhost:50001/Client/Index", "1");
    dynamic receivedData = JsonConvert.DeserializeObject(json);
    Console.WriteLine("Result: {0};",receivedData.data);
}
catch (Exception e)
{
    Console.WriteLine("Oh bother");
    Console.WriteLine();
    Console.WriteLine(e.Message);
}

Basically sends "1" to the Index action in the Client controller.

Here is the Controller:

[HttpPost]
public ActionResult Index(string k)
{
  Debug.WriteLine(String.Format("Result: {0};", k));
  return Json(new { data = k}, JsonRequestBehavior.DenyGet);
}

The result from the Client is just "Result: ;". The debug output from the controller is also "Result: ;". This means that the data is lost somewhere between the client and the site. But when I debug, Visual Studio says that there was one request.

Answer 1

By adding the header and specifying the parameter name, I've managed to get this to work (in your calling method):

 static void Main(string[] args)
        {
            WebClient wc = new WebClient();
            try
            {
                wc.Headers[HttpRequestHeader.ContentType] = "application/x-www-form-urlencoded";
                string json = wc.UploadString("http://localhost:49847/Home/Index", "k=1");
                dynamic receivedData = JsonConvert.DeserializeObject(json);
                Console.WriteLine("Result: {0};", receivedData.data);
            }
            catch (Exception e)
            {
                Console.WriteLine("Oh bother");
                Console.WriteLine();
                Console.WriteLine(e.Message);
            }
        }

From MSDN:

...set the HTTP Content-Type header to application/x-www-form-urlencoded, to notify the server that form data is attached to the post.

I haven't run fiddler to check what (if any) headers are sent through by default but I suspect the reason this doesn't work without the header is the receiving client doesn't know where to find the query string parameters passed through.

From another answer on StackOverflow:

When receiving a POST request, you should always expect a "payload", or, in HTTP terms: a message body. The message body in itself is pretty useless, as there is no standard (as far as I can tell. Maybe application/octet-stream?) format. The body format is defined by the Content-Type header. When using a HTML FORM element with method="POST", this is usually application/x-www-form-urlencoded.

Answer 2

WebAPI may be interpreting your argument as a URI argument.

Try this:

[HttpPost]
public ActionResult Index([FromBody] string k)
{
    Debug.WriteLine(String.Format("Result: {0};", k));
    return Json(new { data = k}, JsonRequestBehavior.DenyGet);
}

This tells WebAPI to expect this argument to be lifted from the body of the request (e.g. a JSON post payload)

Answer 3

Try

            string parameters = string.Concat("k=","1");

            string url = "http://localhost:50001/Client/Index";
            using (Var wc = new WebClient()){

            wc.Headers[HttpRequestHeader.ContentType] = "application/x-www-form-urlencoded;charset=UTF-8";

            string result = wc.UploadString(url, parameters);

            JObject obj = JObject.Parse(result);

            Console.WriteLine("Result: {0};", obj.data);               

            }`